1. Field of the Invention
The invention pertains to the field of shielded cables for use in high speed data transmissions and associated cable retention mechanisms. More specifically, ground receptacles are used in mounting the cables to electrical housings or chassis in a manner that minimizes electromagnetic interference (EMI).
2. Discussion of the Related Art
Cables for use in transmitting electronic signals are often provided with shielding in the form of foil, wire mesh or screen material that surrounds one or more central insulated leads. One common example of this type of cable is the coaxial cable that is used to carry television or data transmissions; however, in computer applications, there are often a plurality of data transfer lines in the form of a cable bundle. The shielding itself is usually covered with an external layer of insulation or a protective outer layer. The shielding protects the wanted signal that is being transmitted on the central lead from ambient electromagnetic disturbances. The shielding also limits the amount of electromagnetic disturbance that is transmitted outwardly from the central lead. For these reasons, shielded cables are increasingly utilized in densely packed arrays of electrical equipment.
A variety of connectors are used to secure and interconnect these cables. Typically, bulkhead connectors, which connect the shielding to a ground proximate the terminus of the cable, are used for shielded cables. Nevertheless, it is not always desirable or practical to connect the cable to ground solely at its terminus. For example, U.S. Pat. No. 5,975,953 to Peterson describes the difficulties and special considerations that are involved when connecting electromagnetic interference (EMI) shielded cables directly to an input/output (I/O) card and having to shunt the ground path through the I/O card.
Further, in the case of bulkhead connectors, a continuing problem exists with securing the cables against unwanted motion that can, for example, cause signal degradation by torsional or translational motion of the cable. Prior systems are unable to secure the cable against unwanted motion while providing a ground for the EMI shielding. Separate structures, such as a rubber grommet that is separate from the bulkhead connector are often used to limit such motion, but constitute poor electrical conductors and may facilitate EMI leaks from an otherwise closed EMI housing.
Regulatory agencies are promulgating ever stricter regulations that increasingly limit the amount of EMI which electronic equipment may generate. Additionally, stricter EMI limits are necessarily imposed by the practicalities of operating computer and telecommunications systems at increasingly faster rates of data transmission. Whenever a cable passes through the wall of an electrical housing or chassis, the opening may provide an unacceptable EMI leak. Increasingly, it is necessary to seal openings electrical housings, in order to prevent EMI leaks. At he same time, it is useful to be able establish EMI seals at multiple optional locations on a single cable construction, to reduce the number of unique cable constructions which would otherwise have to be manufactured and stocked, and to configure these as needed at the time of installation.
The present invention overcomes the problems that are outlined above by providing a mount,, such as a clamp assembly for use in establishing a grounded connection between a shielded cable and a chassis. The grounded connection is located where the grounded connection passes through an electrical housing or chassis and the clamp assembly advantageously seals the EMI enclosure at the point of passage. The clamp assembly advantageously permits the shielded cable to have electronically continuous shielding through the clamp and the chassis.
The clamp assembly comprises a separable block defining at least one aperture. The separable block includes at least two pieces, for example, including a first member that defines a first portion of the aperture and a second member that defines a second portion of the aperture, such that the aperture is completely defined when the first member and the second member are deployed opposite one another. The aperture is appropriately sized to compress the shielded cable for establishing the grounded connection. As used herein, the term xe2x80x9cseparable blockxe2x80x9d includes the use of members that are not connected with one another, as well as blocks where the members are connected by a hinge or pivot to form a bivalve clamp assembly.
The separable block may, for example, comprise a forward face and a rearward face The first member and the second member may comprise complimentary mating structure, such as mirror image complimentary L-shapes, for alignment of the first member and the second member to assist in defining the aperture when the first member and the second member are deployed opposite one another. The two members are held together and compress the cable by means of assembly screws or other fasteners that pass through one member to engage the other.
The first portion of the aperture may comprise a first plurality of pressure ridges, and the second portion of the aperture may comprise a corresponding plurality of second pressure ridges in compressional alignment with the first plurality of pressure ridges. These pressure ridges are used for gripping the shielded cable.
A mounting plate may contain a receptacle that is configured for retaining the first member and the second member in deployment opposite one another. The mounting plate may also contain electromagnetically conductive gasketing which, when compressed by the clamp assembly and its mounting fasteners, forms an electromagnetic seal between the clamp assembly and the mounting plate.
The first member and the second member may each form a generalized L-shape with a leg of the generalized L-shape containing a hole. Respective threaded fasteners may pass through the holes of the legs for use in mounting the first member and the second member onto the mounting plate.
A method of installing the shielded cable provides a secure and reliable grounded connection between a chassis and the separable block. An outer portion of the shielded cable is removed to create an exposed section of electromagnetic shielding; the first member and the second member are placed around the exposed section of electromagnetic shielding such that the exposed section of electromagnetic shielding resides within and contacts the aperture. The first member and the second member are assembled together using screws or other fasteners to compress the electromagnetic shielding within the aperture; this assembly is then inserted into the mounting plate. Threaded fasteners are used to drive the clamp assembly against the mounting plate to compress the electromagnetic gasketing between the clamp assembly and the mounting plate and establish the grounded connection.